This invention relates to a laser cavity optical system for providing beam stabilization from a phasd array semiconductor laser, e.g., a multi-emitter or broad emitter semiconductor laser having a phase locked radiation pattern emitted from a common p-n planar junction.
In U.S. patent application Ser. No. 402,695 filed July 28, 1982 and abandoned in lieu of Ser. No. 637,708 now U.S. Pat. No. 4,530,574, there is disclosed an optical system for focusing the output of a phased array laser into a single spot. Described in this former patent application is a method of focusing a phase locked laser wherein the near field laser spot from such a laser is imaged onto the image plane in the vertical direction, i.e. perpendicular to the plane of the p-n junction, and the far field pattern is imaged in the horizontal direction, i.e. parallel to the plane of the p-n junction. In FIG. 7 of Ser. No. 402,695, there is shown the use of an aperture in the optical system at the lateral far field focal point to eliminate all but the primary lateral field interference lobe since phase locked semiconductor lasers may generally emit several far field lobes. It is usually desirable to focus only the primary far field lobe and the aperture is employed in the optical system to block off nonprominent secondary lobes.
The imaging method proposed in Ser. No. 402,695 for phase locked lasers works well up to a power output of about 75 mW from such a laser at which point, the laser far field pattern shifts causing a "kink" in the power output versus current curves. In the optical system employing an aperture to capture the dominate far field lobe, a beam shift, either in lateral position or angular output, in the far field pattern may cause a shift in the captured dominate far field lobe so that it is no longer aligned with the optical system aperture. What is needed in such an apertured laser cavity optical system is means to prevent such far field beam movement thereby eliminating the need to realing the shifted beam relative to the system aperture for high power laser requirements.